Pituitary tumor cells in tissue culture have been determined in this laboratory to produce not only the hormones which they have been classically known to produce but also a range of one to several other hormones. The purpose of this study is to explore the mechanisms which control the production of hormones by these tumor cells in an effort to improve pathological classification and diagnosis, accuracy of prognosis, prediction of recurrence, and ultimately therapeutic approaches. Cushing's disease is of special interest in this regard.